Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$21.37	11.757%	$23.8825	$23.88	$23.90	$23.90
Purchase #2	$48.90	3.234%	$50.4814	$50.48	$50.50	$50.50
Purchase #3	$160.60	8.168%	$173.7178	$173.72	$173.70	$173.70
Purchase #4	$87.59	10.154%	$96.4839	$96.48	$96.50	$96.50
Purchase #5	$32.89	12.615%	$37.0391	$37.04	$37.05	$37.00
Purchase #6	$185.70	10.436%	$205.0797	$205.08	$205.10	$205.10
Purchase #7	$139.32	4.712%	$145.8848	$145.88	$145.90	$145.90
7 purchase totals =	$676.37		$732.5692	$732.56	$732.65	$732.60